This is kinda what I plan to do with XP and Windows 7 (dual boot).
Slowly migrating games/apps over then testing to see if they work on 7. If they do work I will then delete from XP and resize the 7 partition.
Some older games/apps I have will not run on Vista or 7.
The plan is to eventually have 7 as the main OS with XP just having old games/apps on it.
Two of my coworkers did the Vista 64 to Win 7 x64 upgrade and both are happy with their systems.
I upgraded RC to RTM (64 bit) on my work system and my boss' laptop. The upgrade util told me about two programs that would not function after the upgrade... one required a reinstall, the other only needed a driver reinstalled. Both related to virtual network adapters for VPN programs.
You probably wouldn't be able to completely delete the Windows Vista partition. It is probably THE boot partition which means that Windows 7 will install the necessary files and settings to be able to choose which OS to boot into on to the Vista partition. If you know for a fact (easy to check) that another partition is the boot partition, then yes you would be able to eventually delete the Vista one, although you might then have to run Windows 7's Startup Repair off the DVD because of the now missing partition between the boot one and Windows 7's.
It's easy to upgrade but IMHO it's always better to do a clean install and get rid of all that junk that stocks on your hard drive over time. BTW, if you have a big enough HDD, you can simply install windows on the same partition as the old version and it'll copy everything from the old one into a separate folder from which you can then copy all your settings.
Ep, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS